RECOVERY FROM PNEUMOCYSTIS-CARINII PNEUMONIA IN DEXAMETHASONE-TREATEDWISTAR RATS

Our aim was to study histopathological changes in lung tissue at the l ight microscopic and ultrastructural level during recovery from immuno suppression and Pneumocystis carinii pneumonia. Male Wistar rats were immunosuppressed by per oral dexamethasone for 12 weeks to induce P. c arinii pneumonia, after which dexamethasone was stopped, Recovery was monitored 1, 2 and 4 weeks after cessation of the immunosuppression. I n immunosuppressed animals, CD4+ and CD8+ lymphocytes were both decrea sed in situ. CD8+ lymphocytes increased above control level at week on e, Like CD8+ cells, the ED1+ macrophages increased rapidly in situ. Th is was accompanied by a progressively increasing migration (more trans ient for lymphocytes) of macrophages into bronchoalveolar fluid, assoc iated with morphological signs of activation and phagocytosis and prol iferation of type ZI pneumocytes, Bronchoalveolar lavage (BAL) fluid t umour necrosis factor-alpha (TNF-alpha) increased from subnormal level s to a 4 week peak, with an inverse correlation between TNF-alpha and cyst count (r=-0.626). Our observations suggest a sequence of changes characterized by an increase in CD4+ cells, accompanied by a more rapi d and prolonged recruitment/activation of CD8+ cells, macrophages and type II pneumocytes.